The process of cleaning human dentition with a toothbrush and dentifrice is an important function for both physiological and cosmetic purposes. Human teeth are exposed to a constant flow of saliva and rapidly accumulate a strongly-adherent proteinaceous salivary pellicle which is then colonized by oral bacterial to give rise to dental plaque. Both pellicle and plaque can be stained by a large number of intrinsic and extrinsic materials in the mouth, and if not removed regularly by the mechanical action of toothbrush and dentifrice, can become stained and unsightly. Of equal or greater importance, the presence of plaque on human teeth can lead to serious dental diseases. Some types of plaque contain bacteria which are acid-producing from the degradation of orally ingested carbohydrate foods, and the acid thus produced, along with virulent bacterial cells, can penetrate tooth structure and cause dental decay (caries). Other types of plaque contain bacteria which secrete enzymes that can attack the connective tissues of the human gingiva with the sequelae of tissue inflammation, bleeding, separation of the gingival tissue from the necks of teeth, the development of gingivitis and periodontal disease and in time, the restoration of supporting bony structure followed by the loss of teeth.
Brushing the teeth with a toothbrush alone does not keep the teeth free of stain. Similarly, the use of a dentifrice which lacks adequate abrasive action can result in inadequate cleaning with the subsequent development of cosmetically unacceptable stains.
It has been widely accepted that dentifrices should contain one or more abrasive agents to assist in the cleaning of the dentition. The question of a proper balance of dentifrice abrasivity and safety for human teeth, to avoid excessive wear and erosion of tooth structure, is a subject which has received continuing attention by dental authorities. Based on a comparison of products being tested against a standard, a reading of 250 or less by the Radioactive Dentin Abrasion (RDA) procedure is considered an acceptable level of abrasivity for a dentifrice. The procedure relies on an in vitro technique for irradiating human dentin and then measuring the amount of irradiated dentin removed from the teeth by a dentifrice when brushed on prepared human dentin specimens under standardized and reproducible brushing conditions.
It has been believed heretofore that the cleansing power of a dentifrice is directly proportional to its abrasive level, and that the best-cleaning dentifrices are also the most abrasive products. However, it has been discovered that this parallel relationship is not wholly accurate and it is an objective of this invention to demonstrate that exceptionally powerful cleaning systems can be prepared which have fully acceptable levels of abrasivity as measured by the RDA procedure.
The abrasive characteristics of dentifrice abrasive agents are related to the chemical nature of agents used, their particle size, their hardness and the shape of individual particles.